In recent years, much attention has been given to Silicon Carbide (SiC) semiconductors capable of realizing high breakdown voltage, high current use, low on resistance, high degree of efficiency, power consumption reduction, highspeed switching, etc., since the SiC semiconductors have wider bandgap energy and higher breakdown voltage performance at high electric field, compared with Silicon (Si) semiconductors or Gallium Arsenide (GaAs) semiconductors. The SiC has received attention also in terms of environmental protections since occurrence of carbon dioxide gas (CO2) can be reduced due to the low power consumption performance thereof.
Recently, the SiC devices have been applied to many applicable fields, e.g. air-conditioning apparatuses (air-conditioners), solar power generation systems, automobile systems, and train-vehicle systems.
Since SiC compound semiconductors capable of taking equal to or greater than 200 types of crystal polymorphisms, there may be stable structures different between a substrate (bulk) and an epitaxial growth layer formed on the substrate. Accordingly, the epitaxial growth layer formed on the SiC substrate having an off angle is 0 degree may include many crystal defects. Accordingly, it is general to provide an off angle in the substrate in order to form the SiC epitaxial growth layer.
In such a situation, one of the important problems in a case of applying the SiC is a point of cost. As a detail of the costs of SiC devices, wafer costs account for approximately 50%, SiC epitaxial growth costs account for approximately 22%, and fabrication process costs account for approximately 28%. For example, it is advantageous to use 150-mm (6-inch) φ wafers in terms of reducing the SiC device fabrication costs per unit area. However, it is general to use substrates having an off angle of 4 degrees, as the present 6-inch φ SiC wafers.
One method for a cost reduction of the SiC devices is to reduce such an off angle of the SiC substrate. However, if low-off angle substrates are used, it is difficult to realize high-quality epitaxial growth.
There has also already been reported results of SiC epitaxial growth performed on 4H—SiC substrates having an off angle of 2 degrees, from some groups. According to these reports, doping uniformity and film thickness uniformity can be satisfactorily controlled. However, occurrence of step bunching is increased and a triangular defect density is also increased, compared with SiC epitaxial growth on the SiC substrates having the off angle of 4 degrees. On the other hand, occurrence of the triangular defect can be relatively suppressed under high growth temperatures.